Advances in semiconductor processing and logic design have permitted an increase in the amount of logic that may be present on integrated circuit devices. As a result, computer system configurations have evolved from a single or multiple integrated circuits in a system to multiple hardware threads, multiple cores, multiple devices, and/or complete systems on individual integrated circuits. Additionally, as the density of integrated circuits has grown, the power requirements for computing systems (from embedded systems to servers) have also escalated. Furthermore, software inefficiencies, and its requirements of hardware, have also caused an increase in computing device energy consumption. In fact, some studies indicate that computing devices consume a sizeable percentage of the entire electricity supply for a country, such as the United States of America. As a result, there is a vital need for energy efficiency and conservation associated with integrated circuits. These needs will increase as servers, desktop computers, notebooks, Ultrabooks™, tablets, mobile phones, processors, embedded systems, etc. become even more prevalent (from inclusion in the typical computer, automobiles, and televisions to biotechnology).
Energy and power efficiency are key issues in computer systems, from small portable devices to large data centers. However, many modern processors are typically optimized for performance and inefficiency in energy/power control is less addressed. In modern processors, power management is often performed by special controller. This controller uses a model to evaluate system inputs such as performance events to make a decision as to power state for the processor. The power management model can be either analytical or statistical, but is typically static and requires a priori knowledge of a system. The model is developed during design stage and is not changeable after shipment. In order for the model to work well across a wide range of applications, the model is set conservatively, and thus is not optimal in many situations.